1. Field of the invention
The invention concerns an optical system for connecting customer premises networks to a switching center of a telecommunication network providing interactive and non-interactive services. An optical connection system has a wide bandwidth enabling customer premises networks to use services available on a broadband telecommunication network. There are two types of service: interactive services such as data transmission and telephony, with variants such as three-way conference calls, and non-interactive services using one-way transmission and usually broadcast to a wide audience. A typical example of a large scale broadcast service is the broadcasting of audio or video programs.
2. Description of the prior art
French patent application no. 91 12 264 describes an optical connection system to a telecommunication network which can provide interactive services and which could also provide non-interactive services. In this system each customer premises network is connected by an optical fiber to a distribution network which is in turn connected by a number of optical fibers to units called central office termination equipments in the switching center. Each central office termination equipment comprises an optical sender and an optical receiver operating at the same fixed wavelength. Each central office termination equipment uses a different wavelength. Each customer premises network comprises an optical sender and an optical receiver which can be tuned to different wavelengths. A wavelength is assigned to a customer premises network by a control unit in the switching center at the time each call is set up between the installation and a central office termination equipment. The number of customer premises networks is very much larger than the number of central office termination equipments to which they are connected because not all customer premises networks make or receive calls simultaneously. Dynamic assignment of wavelengths to customer premises networks means that the same wavelength can be used again for different customer premises networks setting up non-simultaneous calls. The group of central office termination equipments connected to the same broadcast network comprises a number of central office termination equipments limited by the number of wavelengths that can be used for sending and receiving, which is a limitation of the available technology.
A group of customer premises networks is connected to a group of central office termination equipments by a distribution network which broadcasts an optical signal sent by any sender of the connection system to each optical receiver of the connection system. A switching center may comprise a plurality of identical connection systems each comprising a group of central office termination equipments connected to a group of customer premises networks by independent broadcast networks so that a common set of wavelengths can be re-used several times.
A control central office termination equipment in each group of central office termination equipments sets up calls. When a customer premises network goes active, it sends a message using the control central office termination equipment wavelength. The control central office termination equipment sends the message to the control means of the switching center. The control means tell the control central office termination equipment the identity of a central office termination equipment available to set up a call. The control central office termination equipment sends a message to the customer premises network using the control central office termination equipment wavelength. This message tells the customer premises network the identity of the available central office termination equipment. The customer premises network deduces from this the wavelength of the available central office termination equipment. This wavelength is assigned to this customer premises network for the entire duration of this call, and for this duration only.
To use a non-interactive service a customer premises network would request the control central office termination equipment to set up a call between it and the means supplying the signals of the non-interactive service requested. The control means of the switching center command the setting up of a connection in the connection network to connect an available central office termination equipment other than the control central office termination equipment to the requested service. The number of central office termination equipments busy with the same service is the same as the number of customer premises networks that have requested the service. This connection system is therefore not well suited to non-interactive services because it would require a number of central office termination equipments similar to the number of customer premises networks if a non-interactive service were requested simultaneously by a large majority of customer premises networks.
An object of the invention is to improve this system so that it is able to provide non-interactive services realistically, without increasing the number of central office termination equipments as compared with the situation in which the system provides only interactive services, in which case it is possible to use a number of central office termination equipments very much smaller than the number of customer premises networks given that such calls always represent a very small amount of traffic, in the order of 0.05 erlangs, for example.